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The shield most used in practice are those that expand the communication of the Arduino board and in particular those that allow to add a network connection to a TCP / IP.

The first shield of this kind were those based on Ethernet technology, which helps the Arduino to connect to a LAN based on Ethernet TCP / IP, and so to Internet.

The convenience of Wi-Fi is now known to all: no more cables to spread (which increases the cost and time of construction of any plant) and full freedom in the positioning of the different nodes of the wireless network.

One of the first companies to focus on Wi-Fi was theAsyncLabs, who proposed a famous WiFi shield, including the appropriate libraries.

What we propose is a new solution for Wi-Fi: this is a shield that the hardware was inspired by that of AsyncLabs, but in addition, we have provided a slot for microSD memory.

The basic component of the shield that we have made is a Wi-Fi moduleMRF24WB0MAmanufactured by Microchip.

The device is a Wi-Fi IEEE 802.11 RF transceiver, with a data rate between 1 and 2 Mbps, and with an internal antenna.

The WiFi shield supports both types of wireless networks infrastructure (BSS) and ad-hoc (IBSS) and is also allowed to connect to secure networks (cryptographers and are supported 64 and 128-bit WEP, WPA/WPA2 and TKIP, AES and PSK).

In our project is using the SPI connection for communication with the WiFi controller through the SDO, SCK and SDI (pin 32, 34 and 35) and, if necessary, can be reset using a button (P1 in the diagram).

Peculiarities of our shield is that it has a SD card slot (SD1 signed in the schematic), managed by Arduino always through the SPI port.

There is also a LED (LD1 signed) used to indicate whether the Wi-Fi is active or not, its management is implemented through a hardware port, so you usually can not be used by software. In the event that was needed precisely this port, you still have a jumper that, when opened, making it available again disconnect the LED pin I / O.

Finally, to complete the hardware of the shield there is a section dedicated to the power, consists of a 3.3 Vvoltage regulator(indicated with U2).